Turbines Could Tap the Mississippi's Power

Underwater turbines could harness a massive amount of energy—but could cause problems for boat navigation.

Tens of thousands of turbines anchored to the bottom of the Mississippi River could someday provide more than a gigawatt of renewable energy, enough to power a quarter of a million homes. That’s the vision of Free Flow Power, a startup based in Gloucester, Massachusetts, that recently received preliminary permits from the U.S. Federal Energy Regulatory Commission (FERC) granting it the right to explore energy production at dozens of sites along the lower Mississippi over the next three years.

Power Up: Free Flow Power hopes to deploy tens of thousands of underwater turbines in the Mississippi River. That many turbines could generate enough power for a quarter million homes.

The proposed development is one of a number of “hydrokinetic” projects in the works. Such projects seek to generate electricity from wave movement, tidal flows, or river currents, without the use of dams.

The ambitious Mississippi project, however, relies on relatively unproven technology. The only commercial hydrokinetic river-power system operating in the U.S. is a single turbine deployed by Hydro Green Energy close to a conventional hydropower dam on the Mississippi River in Hastings, Minnesota.

Free Flow hopes to deploy hydrokinetic power on an unprecedented scale: hundreds of 40-kilowatt turbines, each the size and shape of a large jet engine and attached to pylons jutting out from the riverbed at 88 locations along the Mississippi.

Although most companies developing hydrokinetic technology have focused on tidal or wave energy, Free Flow’s chief financial officer, Henry Dormitzer, argues that river power has distinct advantages. “The water flows in one direction, it doesn’t have salt in it, and, in the case of the Mississippi, people have spent 100 years tracking water flows and velocities,” he says.

But the Mississippi is also one of the world’s busiest waterways, and the company will have to demonstrate that its turbines will not interfere with commercial shipping, and that it will have no negative impact on the river’s wildlife.

In July 2009, Free Flow began a six-month test of a pilot turbine (a third the size of the planned commercial ones) in the Mississippi, and the company is now testing a commercial-scale prototype in the lab. Free Flow has also received $7.4 million in funding from investors and from the U.S. Department of Energy that will allow it to test its most recent prototype in the Mississippi next year. Free Flow Power is seeking additional funding to test four turbines, each attached to a separate pylon, over a 12-month period, as required by FERC as part of the licensing process.

Free Flow uses a “shrouded turbine” design that channels water through the turbine’s blades. Water passes through a rotor with seven blades that are designed for a slow spin rate to minimize fish strikes. The turbines will be sited 10 or more feet off the riverbed. At this depth, water moves, on average, at one to three meters per second.

A 2007 study by the Electric Power Research Institute in Palo Alto, California, predicted that the U.S. could develop three gigawatts of hydrokinetic power from rivers by 2025. That’s the equivalent of roughly two new nuclear power plants. “There is no question the potential for hydrokinetic river power is huge, but this industry is so young, it’s very hard to say how economically viable it will be,” says Andrea Copping, a senior program manager at Pacific Northwest National Laboratory in Sequim, Washington.

Copping says hydrokinetic power needs a strong commitment from commercial and government interests if it’s to take off. “Unless there are public funds to help get this industry off the ground, we are not going to have an industry,” she says. “Right now the early developers are being hit with really expensive studies, because the FERC doesn’t know what the problems are, so they want the individual companies to look at all potential problems.”

Michael Bahleda, an energy consultant with U.K.-based Halcrow Group, says securing the funding needed to carry out the necessary studies may prove difficult. “Until you get through the licensing process, investors aren’t going to commit a lot of money,” he says. “As it stands now, the permitting and licensing is very time-consuming. It’s hard to attract capital until you are further along in that process.”

Bahleda also questions whether some of the chosen sites along the Mississippi will prove viable, either because of insufficient water-flow rates or because of regulatory issues related to shipping and the environment.

The biggest environmental challenge will be preventing direct strikes to fish and other organisms. Even if individual turbines cause only a small number of strikes, the sheer size of Free Flow’s proposed project raises significant concerns, says U.S. Fish and Wildlife Service biologist Joyce Collins, who is working with Free Flow to study strike issues. Collins says the company will have to pay particular attention to an endangered species that lives in the Mississippi called the pallid sturgeon.

Free Flow Power will also have to convince barge operators that their turbines won’t interfere with commercial traffic. “There are times where you can have a low-water period where there is only 10 to 20 feet from the bottom to the top of the water; if you have pylons installed in certain areas, a vessel could run into them,” says Mark Wright, vice president of the American Waterways Operators, a trade group representing the tugboat, towboat, and barge industry.

Edward Lovelace, Free Flow Power’s vice president of engineering, says all of the sites selected by Free Flow Power will have sufficient clearance above them even during periods of low water. Drawing on historical flow data from the Mississippi, the company selected sites that maintained a depth of at least 40 feet during approximately 100-year lows. Such sites would allow for a minimum of 20 feet of water above the tops of the turbines for barges that draw no more than 14 feet of water.